1. Field of the Invention
The invention relates to a monitoring device for a fuel injection amount control apparatus.
2. Description of Related Art
A fuel injection amount control apparatus for an engine that is mounted in a vehicle or the like drives injectors of the engine based on an injection amount command value calculated by a calculation unit, thereby controlling the amount of fuel injection by the injectors. At the time of normal engine operation, for example, after the completion of warm-up of the engine, the calculation unit of the fuel injection amount control apparatus obtains a basic injection amount based on an operation state of the engine such as an accelerator operation amount and an engine rotational speed, and assigns the basic injection amount to the aforementioned injection amount command value to calculate the injection amount command value.
Besides, in Japanese Patent Application Publication No. 2013-238203 (JP 2013-238203 A), there is described a monitoring device that determines whether or not there is an abnormality in the aforementioned calculation unit in the fuel injection amount control apparatus. This monitoring device calculates a monitoring injection amount equivalent to the aforementioned basic injection amount, based on the operation state of the engine such as the accelerator operation amount and the engine rotational speed, in parallel with calculation of the injection amount command value by the aforementioned calculation unit. Then, when the injection amount command value calculated by the aforementioned calculation unit deviates, in an increasing manner, from the aforementioned monitoring injection amount, the monitoring device determines that an abnormality has occurred in a function of calculating the injection command value in the aforementioned calculation unit.
Incidentally, the aforementioned accelerator operation amount is detected through the use of an accelerator position sensor, and the aforementioned engine rotational speed is detected through the use of a crank angle sensor. Incidentally, this accelerator position sensor and this crank angle sensor have a function of detecting a sensor abnormality, and can output a detection signal that is guaranteed to be natural, with the aid of the function.
By the way, the calculation unit of the fuel injection amount control apparatus obtains a start-up injection amount for enhancing the startability of the engine based on a cooling fluid temperature of the engine that is detected by a fluid temperature sensor from the start of start-up of the engine to the completion of start-up, and assigns the start-up injection amount to the injection amount command value to calculate the injection amount command value. Furthermore, after the completion of start-up of the engine, the aforementioned calculation unit assigns the larger one of the aforementioned start-up injection amount that decreases as the cooling fluid temperature of the engine rises, and the aforementioned basic injection amount that is obtained based on the operation state of the engine, to the injection amount command value, thereby calculating the injection amount command value.
On the other hand, it is preferable that the monitoring device determine whether or not there is an abnormality in the aforementioned calculation unit, immediately after the completion of start-up of the engine. It should be noted, however, that when the device calculates the aforementioned monitoring injection amount, sensors that do not have the function of detecting the presence of an abnormality upon the occurrence thereof, such as the fluid temperature sensor and the like, namely, sensors incapable of detecting a detection signal that is guaranteed to be normal cannot be employed to calculate the aforementioned monitoring injection amount. For this reason, the aforementioned monitoring injection amount cannot be calculated as a value equivalent to the start-up injection amount, based on the cooling fluid temperature detected by the fluid temperature sensor. Accordingly, at this time as well, the monitoring injection amount must be calculated through the use of sensors capable of outputting a detection signal that is guaranteed to be normal, such as the accelerator position sensor, the crank angle sensor and the like. There is no choice but to calculate the monitoring injection amount equivalent to the aforementioned basic injection amount, through the use of such sensors.
Therefore, in the case where the start-up injection amount becomes larger than the basic injection amount as a result of lowness of the cooling fluid temperature of the engine immediately after the completion of start-up of the engine and the start-up injection amount is assigned to the injection amount command value, even when the calculation unit is normal, the injection amount command value (equivalent to the start-up injection amount) deviates, in an increasing manner, from the monitoring injection amount (equivalent to the basic injection amount). Then, it may be erroneously determined, based on this deviation between the injection amount command value and the monitoring injection amount, that an abnormality has occurred in the calculation unit.
FIG. 8 is a time chart showing changes in the start-up injection amount, the basic injection amount and the injection amount command value from the start of start-up of the engine to the completion of start-up. As is apparent from the drawing, after the completion of start-up of the engine, while the larger one of the basic injection amount and the start-up injection amount is adopted as the injection amount command value (indicated by a broken line), the monitoring injection amount is calculated as a value equivalent to the basic injection amount. Therefore, when the start-up injection amount is larger than the basic injection amount, for example, immediately after the completion of start-up of the engine or the like, the injection amount command value may greatly deviate, in an increasing manner, from the monitoring injection amount in spite of normal calculation of the injection amount command value (equivalent to the start-up injection amount), and it may be erroneously determined, based on the deviation, that an abnormality has occurred in the calculation unit for calculating the injection amount command value.